In a Q-switch laser, laser oscillation is suppressed by incorporating a special kind of shutter (Q switch) inside an optical resonator so that when a large amount of energy has been built up in the laser medium and this Q switch is opened, a single pulsed laser with a short pulse width and a high peak value can be realized. Therefore, by opening and closing a Q switch at a suitable cycle, it is possible to achieve a pulsed laser beam which is generated intermittently in synch with this cycle.
In a Q-switch laser, which generates a cyclic pulsed laser beam like this, as shown in FIG. 4, the first pulsed laser after the release of laser output stoppage (hereafter referred to as a giant pulse) consists of an extremely larger amount of energy than the second and subsequent pulsed lasers, and if this giant pulse is used as-is for processing, it causes processing defects. For this reason, in the various processing devices that utilize this kind of Q-switch laser, a variety of contrivances have been devised so that this giant pulse is not used to carry out processing.
For example, IN a laser marking device, which displays a required marking pattern on a liquid crystal mask, and marks a product number, manufacturing date, lot number and serial number on integrated circuit (IC) packages by irradiating a laser beam through this liquid crystal mask onto the IC package to be processed, a laser scatterer is provided at the edges of the liquid crystal mask, so that by directing the giant pulse at this laser scatterer, the giant pulse is scattered, and the giant pulse is not used in the marking process.
Meanwhile, there is a close relationship between laser output value and processing quality in various processing equipment which utilize the Q-switch laser described above. Monitoring laser output is important for maintaining process quality. Furthermore, this laser output value is an important parameter for determining the service life of various expendable items.
Thus, this type of Q-switch laser is ordinarily equipped with an average value measurement function, which measures the average output of a pulsed laser. As the prior art thereof, there is the Japanese Patent Application Laid-open No.1-124722.
In this prior art, the average output of a Q-switch pulse laser is measured by multiplying the peak value (peak value) of a pulsed laser beam and the half-value width of a pulsed laser beam by the frequency of a Q-switched laser pulse.
However, with this prior art, since the above-described giant pulse is not taken into consideration when measuring the average output, an accurate average value measurement cannot be made when this prior art is utilized in processing equipment in which giant pulses are not used to perform processing. This results in problems which adversely affect process quality and the determination of expendable item service life.
Furthermore, there are problems in the above-described prior art. Because a portion of a laser output is isolated via a beam splitter, and this isolated laser beam is attenuated via an attenuator, the average output of the laser is sought based on this attenuated laser beam. This reduces the laser output used in processing, making it impossible to utilize laser output efficiently. Another problem is that because of the existence of a beam splitter and attenuator, the laser device has a complex configuration and is costly.
With the foregoing in view, it is an object of the present invention to provide a pulse laser, which accurately measures the average output of a pulsed laser by eliminating the influence of giant pulses.
It is also an object of the present invention to provide a pulse laser, which is capable of measuring the average laser output using a simple configuration that does not reduce the laser output used in processing.